To prevent discharge of HC to the outside of a vehicle by premixed compression ignition, the deterioration in fuel economy and an increase in an HC discharge quantity by useless fuel addition in a temperature area of the low NOx reduction ratio.

This exhaust emission control device has temperature sensors 23 and 24 for detecting the exhaust temperature in a proper position of an exhaust pipe 11 as a substitute value for estimating the catalyst bed temperature of a selective reduction type catalyst 13, and has a control device 22 for permitting premixed compression ignition control only when estimating that the catalyst bed temperature of the selective reduction type catalyst 13 is the active temperature or more based on a detection value of the temperature sensors 23 and 24, permitting fuel addition only when its estimated catalyst bed temperature of the selective reduction type catalyst 13 falls within an effective temperature range sandwiched between a high temperature area unable to provide the required NOx reduction ratio and a low temperature area of not expecting sure combustion of fuel and controlling a fuel adding quantity so that the adding fuel/NOx ratio becomes a right optimal value in response to the NOx reduction ratio in its estimated catalyst bed temperature of the selective reduction type catalyst 13.

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